The development of ever-larger multi-section telescopic crane booms has created structural and operational problems which have not existed in comparatively smaller crane booms of lesser load lifting capacities. Among these problems is an increased tendency for the extended boom to deflect laterally due to stresses caused by a supported swinging load, as when the boom is in a sluing mode. There is also an increased tendency for buckling of the side and top plates of the boom sections due to twisting stresses including those induced by the weight and the rigging of a side stowable jib for the multi-section boom.
It is the object of the present invention to deal effectively, economically and practically with these problems through the provision of lateral supports for the top plates of movable boom sections in both their fully retracted and fully extended positions, which are the only positions of use in the largest sizes of multi-section booms.
The provided lateral supports are active only when the boom sections are fully retracted and fully extended. In the latter case, the supports are active in the critical socketing zone between adjacent boom sections. The supports are individually adjustable to regulate the lateral clearance between adjacent boom sections. The supports form a spacing mechanism which augments the action of the customary bottom lateral wear pads on booms of this character.
The bottom lateral wear pads support the rears of the extended boom sections, but heretofore in the prior art nothing has been provided to restrict lateral play at the tops of the boom sections in the socketing area. The present invention effectively restricts this top lateral movement or play at the front of the socketing area to prevent side deflection or buckling, as stated.
Other features and advantages of the invention will become apparent during the course of the following detailed description.